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On this page are computer-accessible forms for the graph C4[ 21, 2 ] = PS(3,7;2).

(I) Following is a form readable by MAGMA:

g:=Graph<21|{ {13, 15}, {10, 15}, {1, 9}, {5, 13}, {4, 12}, {3, 11}, {2, 10}, {6, 14}, {2, 8}, {7, 13}, {3, 9}, {5, 15}, {6, 12}, {4, 15}, {4, 10}, {5, 11}, {1, 14}, {7, 8}, {2, 19}, {4, 21}, {1, 19}, {1, 18}, {5, 16}, {7, 18}, {2, 20}, {7, 17}, {3, 21}, {6, 16}, {3, 20}, {6, 17}, {8, 17}, {12, 21}, {10, 19}, {9, 18}, {11, 16}, {8, 20}, {9, 21}, {12, 17}, {14, 19}, {14, 16}, {11, 20}, {13, 18} }>;

(II) A more general form is to represent the graph as the orbit of {13, 15} under the group generated by the following permutations:

a: (3, 7)(4, 15)(5, 12)(6, 16)(8, 20)(9, 18)(11, 17)(13, 21)
b: (2, 3, 16, 13, 10, 21, 6, 7)(4, 12, 17, 8, 20, 11, 5, 15)(9, 14, 18, 19)
c: (1, 2)(3, 7)(4, 6)(8, 9)(10, 14)(11, 13)(15, 16)(17, 21)(18, 20)

(III) Last is Groups&Graphs. Copy everything between (not including) the lines of asterisks into a plain text file and save it as "graph.txt". Then launch G&G (Groups&Graphs) and select Read Text from the File menu.

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&Graph
C4[ 21, 2 ]
21
-1 14 18 19 9
-2 8 19 20 10
-3 11 9 20 21
-4 12 15 10 21
-5 11 13 15 16
-6 12 14 16 17
-7 13 17 18 8
-8 2 17 7 20
-9 1 3 18 21
-10 2 4 15 19
-11 3 5 16 20
-12 4 6 17 21
-13 15 5 7 18
-14 1 16 6 19
-15 13 4 5 10
-16 11 14 5 6
-17 12 6 7 8
-18 1 13 7 9
-19 1 2 14 10
-20 11 2 3 8
-21 12 3 4 9
0

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